Exposure to room lighting during sleep may impair blood sugar and cardiovascular regulation

Close blinds, draw curtains and turn off all lights before bed: Exposure to even moderate ambient lighting during nighttime sleep, compared to sleeping in a dimly lit room, impairs your cardiovascular function during sleep and increases your insulin resistance the next morning, reports a new study from Northwestern Medicine published in PNAS.

The results of this study demonstrate that a single night of exposure to moderate ambient light during sleep can impair blood sugar and cardiovascular regulation, which are risk factors for heart disease, diabetes and metabolic syndrome. It is important for people to avoid or minimize the amount of light exposure during sleep.”


Phyllis Zee, MD, PhD, chief of sleep medicine in the Department of Neurology Ken and Ruth Davee, physician at Northwestern Medicine and senior study author

There is already evidence that exposure to light during the day increases heart rate via activation of the sympathetic nervous system, which kicks your heart into high gear and increases alertness to meet the challenges of the day.

“Our results indicate that a similar effect is also present when light exposure occurs during nocturnal sleep,” Zee said.

The heart rate increases in a lighted room and the body cannot rest properly

“We have shown that your heart rate increases when you sleep in a moderately lit room,” said Daniela Grimaldi, MD, PhD, study co-first author and research assistant professor of neurology in the division of sleep medicine. . “Even if you’re sleeping, your autonomic nervous system is activated. That’s bad. Usually your heart rate and other cardiovascular parameters are lower at night and higher during the day.”

There are sympathetic and parasympathetic nervous systems that regulate our physiology during the day and night. The sympathetic takes charge during the day and the parasympathetic is believed to control the physiology at night, when it transmits restoration to the whole body.

How nighttime light while sleeping can lead to diabetes and obesity

Investigators found that insulin resistance occurred the morning after people slept in a bright room. Insulin resistance occurs when your muscle, fat, and liver cells don’t respond well to insulin and can’t use glucose from your blood for energy. To compensate for this, your pancreas makes more insulin. Over time, your blood sugar rises.

An earlier study published in JAMA Internal Medicine looked at a large population of healthy people who were exposed to light while sleeping. They were more overweight and obese, Zee said.

“Now we’re showing a mechanism that could be fundamental to why this happens. We’re showing that it affects your ability to regulate glucose,” Zee said.

Study participants were unaware of biological changes in their bodies at night.

“But the brain feels it,” Grimaldi said. “It acts like the brain of someone with light and fragmented sleep. Sleep physiology is not resting as it should.”

Exposure to artificial light at night during sleep is common

Exposure to artificial light at night during sleep is common, whether from indoor electroluminescent devices or from sources outside the home, especially in large urban areas. A significant proportion of individuals (up to 40%) sleep with a bedside lamp on or with a light on in the bedroom, or keep the television on.

Light and its relationship to health are a double-edged sword.

“In addition to sleep, nutrition and exercise, light exposure during the day is an important factor for health, but during the night we show that even modest light intensity can alter measurements of heart and endocrine health,” Zee said.

The study tested the effect of sleeping with 100 lux (moderate light) versus 3 lux (low light) in participants over a single night. Investigators found that moderate exposure to light puts the body into a higher state of alert. In this state, the heart rate increases along with the force with which the heart contracts and the rate at which blood is driven to your blood vessels for oxygenated blood flow.

“These findings are particularly important for those living in modern societies where exposure to indoor and outdoor nighttime light is increasingly prevalent,” Zee said.

Zee’s Top Tips for Dimming Light While Sleeping

  1. Don’t turn on the lights. If you need to have a light on (which older people may want for safety), make it a dim light closer to the ground.
  2. Color is important. Amber or a red or orange light is less stimulating for the brain. Do not use white or blue light and keep it away from the sleeping person.
  3. Blackout blinds or eye masks are good if you can’t control outside light. Move your bed so outside light doesn’t shine on your face.

Is my bedroom too bright?

“If you’re able to see things well, it’s probably too clear,” Zee said.

Other Northwestern authors are co-first author Ivy Mason, PhD, who at the time of the study was a postdoctoral fellow at Northwestern and is now a research fellow at Harvard Medical School; Kathryn Reid, PhD, research professor of neurology in the division of sleep medicine; Chloe Warlick; Roneil Malkani, MD, associate professor of neurology in the division of sleep medicine; and Sabra Abbott, MD, PhD, assistant professor of neurology in the division of sleep medicine.

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